Network registration and network slice selection system and method

ABSTRACT

Implementations of a registration procedure are described. The registration procedure includes a Access and Mobility Function (AMF) selection procedure and a Session Management Function (SMF) selection procedure. The AMF receives a Non-Access Stratum (NAS) registration request pertaining a User Equipment (UE). At least partially in response to the registration request: the AMF registers the UE on the network; and establishes a Protocol Data Unit (PDU) session for the UE. The AMF transmits a registration response to the UE. An access node of the network receives a Radio Resource Control (RRC) registration request from a User Equipment (UE). At least partially in response to the registration request: The access node selects an AMF, and forwards a corresponding Non-Access Stratum (NAS) registration request to the selected AMF. The NAS registration request includes PDU session request information pertaining to the UE.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is related to U.S. Provisional Patent Application Ser.No. 62/455,380, filed Feb. 6, 2017, and U.S. Provisional PatentApplication Ser. No. 62/472,739, filed Mar. 17, 2017 the contents ofwhich are incorporated herein by reference.

FIELD

The present application pertains to the field of communication networksand in particular to systems and methods for registering a UserEquipment (UE) to a network slice supported by a communication network.

BACKGROUND

A communication network (or simply a “network”) refers to a collectionof communicatively coupled devices which interoperate to facilitatecommunication between various endpoint devices, such as User Equipmentdevices. The term “User Equipment” (UE) is used herein for clarity torefer to endpoint devices which are configured to communicate with anetwork either via fixed line connection, or via radios operatingaccording to a predetermined protocol. The UE includes a variety ofconnected devices including UEs as defined by the 3^(rd) Generationpartnership project (3GPP), mobile devices (e.g. wireless handsets) andother connected devices, including Machine-to-Machine (M2M) devices(also referred to as Machine Type Communications (MTC) devices). Amobile device need not be mobile itself, but is a device that cancommunicate with a network which is capable of providing communicationservices in the same mode whether or not the endpoint device is mobileor stationary. A network may include, for instance, at least one of aradio access portion which interfaces directly with UEs via radio accessand a fixed line portion which interfaces directly with UEs via fixedline access, in combination with a backhaul portion which connectsdifferent network devices of the network together. The network mayfurther comprise various virtualized components as will become readilyapparent herein. A primary forward looking example of such a network isa Fifth Generation (5G) network. The present application relates toinventive improvements and additions to, among other works, 3GPPSpecification #23.501, “System Architecture for the 5G System”, thecontents of which are incorporated herein by reference.

It has been proposed that 5G networks be built with various networktechnologies that allow for the network to be reconfigured to suitvarious different needs. These technologies can also allow the networkto support network slicing to create different sub-networks withcharacteristics suited for the needs of the traffic they are designed tosupport. The network may include a number of computing hardwareresources that provide processors and/or allocated processing elements,memory, and storage to support functions executing on the network, aswell as a variety of different network connectivity options connectingthe computing resources to each other, and making it possible to provideservice to mobile devices.

A service generally corresponds to a source, or a sink, for specifieddata communications that is available on the network. Accessing aservice may involve communication between multiple endpoints that areconnected to the network. A service may be provided by the networkoperator, or may be provided by network customer such as a business,utility, government, or other organization. Examples of servicesinclude, but are not limited to, providing audio and/or video content tostream or download to an endpoint such as a UE, storage and/orprocessing of data from an endpoint such as a UE, UE-to-UE messagingservices, machine-to-machine communications such as utility meterreporting, remote data storage, and/or remote computing services.

A network slice generally corresponds to a set of network resourceswhich have been allocated to support at least one specific service onthe network. Such network resources may include cloud-basedcommunication, computing and memory resources, physical connection andcommunication resources, wireless radio access resources such asfrequency, time and code multi-access resources, telecommunicationresources, memory resources and computing resources.

A UE seeking access to a service, may seek to connect directly to thatservice, or in some embodiments to a network slice that supports theservice. The process of connecting a UE to a service and/or networkslice starts with the step of registering the UE. Registration may beinitiated through a radio access node (R)AN that is currently providingconnection between the UE and the network.

A network entity generally refers to a network node, or a combination ofnetwork nodes, that is operative to provide specified services on thenetwork. A network entity comprises physical components, such asprocessors, allocated processing elements, or other computing hardware,computer memory, communication interfaces, and other supportingcomputing hardware. The network entity may use dedicated physicalcomponents, or the network entity may be allocated use of the physicalcomponents of another device, such as a generic computing device orresources of a datacenter, in which case the network entity is said tobe virtualized. A network entity may be associated with multiplephysical components that may be located either in one location, or maybe distributed across multiple locations.

A network function comprises a service that may be provided by a networkentity, or may comprise physical components configured in a certain wayto provide a given functionality, which may be described in terms ofdata inputs and outputs. In general, a network entity may be operativeto support one or more network functions on the network. In someembodiments, the network entity may be abstracted across multiplephysical locations of the network, for instance by execution at aplurality of network nodes, to operate in a coordinated fashion bycollecting, processing, directing, and/or acting to provide theservice(s) required of that network entity.

In proposed 5G networks, it is intended that the operator will becapable of deploying multiple network slices to support differentservices. Accordingly, the network operator can decide whether a singleslice or multiple network slices are required. For example, an operatormay support service types A and B within a single slice, or it mayprovide service type A in slice 1 and service type B in slice 2.

In order for a UE to gain access to a service operated by the network,it must register. To maintain flexibility for the network operator, itmay be desirable to provide a registration procedure that is able tosupport a plurality of different deployment options to accommodate thedifferent slice and service offerings.

Therefore, there is a need for a system and method for registering a UEto a network service or network slice that is not subject to one or morelimitations of the prior art.

This background information is provided to reveal information believedby the applicant to be of possible relevance to the present application.No admission is necessarily intended, nor should be construed, that anyof the preceding information constitutes prior art against the presentapplication.

SUMMARY

In an implementation, a method is provided for registering a UserEquipment (UE) for connection to a service available on a network. Themethod may include: receiving a registration request from the UE;selecting an access and mobility function (AMF) of the network based onthe registration request; transmitting the registration request to theselected AMF; receiving a registration response from the selected AMF;and, transmitting the received registration response to the UE.

Accordingly, an aspect of the present invention provides a method in anaccess and mobility function (AMF) of a network, the method comprising:receiving, by the AMF, a Non-Access Stratum (NAS) registration requestpertaining a User Equipment (UE) connected to the access node; at leastpartially in response to the registration request: registering the UE onthe network; and establishing a Protocol Data Unit (PDU) session for theUE, based on information contained in the registration request; andtransmitting, by the AMF, a registration response to the UE.

A further aspect of the present invention provides a method in an accessnode of a network, the method comprising: receiving, by the access node,a Radio Resource Control (RRC) registration request from a UserEquipment (UE) connected to the access node; at least partially inresponse to the registration request: selecting an access and mobilityfunction (AMF) based on information in the received registrationrequest; and subsequently forwarding a corresponding Non Access Stratum(NAS) registration request to the selected AMF, the NAS registrationrequest including PDU session request information pertaining to the UE.

A further aspect of the present invention provides a User Equipment (UE)comprising: at least one processor; and a non-transitory computerreadable storage medium storing software instructions configured tocontrol the at least on processor to: generate a Radio Resource Control(RRC) registration request for registering the UE for connection to aservice available on a network, the registration request furtherincluding PDU session request information; transmit the RRC registrationrequest to an access point of the network; and subsequently receive aregistration acknowledgment from an access and mobility function (AMF)of the network.

BRIEF DESCRIPTION OF THE FIGURES

Further features and advantages will become apparent from the followingdetailed description, taken in combination with the appended drawings,in which:

FIG. 1 is a signalling diagram illustrating an embodiment of aregistration procedure.

FIG. 2 is a signalling diagram illustrating an embodiment of AMF and SMFselection.

FIG. 3 is a signal flow diagram of an embodiment of registrationsignalling.

FIG. 4 is a block diagram of an embodiment of an AMF configuration.

FIG. 5 is a block diagram of an embodiment of an AMF configuration.

FIG. 6A is a signalling diagram illustrating an embodiment of aregistration procedure.

FIG. 6B is a signalling diagram illustrating an embodiment of aregistration procedure.

FIG. 7 is a signaling diagram illustrating an embodiment of UEregistration with AMF relocation.

FIG. 8 is a block diagram of an embodiment of a computing system.

It will be noted that throughout the appended drawings, like featuresare identified by like reference numerals.

DETAILED DESCRIPTION

In an implementation, this application describes a registrationprocedure for use when using the Network Slice Selection AssistanceInformation (NSSAI). The registration procedure includes the Access andMobility Function (AMF) selection procedure and the Session ManagementFunction (SMF) selection procedure. This invention provides details ofthe information that is required to perform the registration procedure.The content of the Radio Resource Control (RRC) and Non-Access Stratum(NAS) Request and Response messages are described.

It is desirable that any network slice configuration system providessufficient flexibility to configure network slices to support a varietyof specific services. In some implementations, however, it may be usefulthat the deployment configuration satisfies the following constraints:

-   A UE should be able to attach to multiple network slices with a    single AMF-   AMFs may be common to a set of network slices-   In some implementations, the slice specific functions (e.g. SMFs and    UPFs) should not be shared, and instead each be dedicated to a    specific slice-   Each network slice, described by an SST/SD, should only be    associated with a single network slice group.

Given the above constraints, it is possible to configure Network SliceGroups (NSGs) where each group is isolated from the other groups. Insome implementations, an NSG identifier (NSGI) may be configured in theUE by the Home Public Land Mobile Network (HPLMN). The UE may provide aconfigured NSGI in the RRC message during the initial Registrationprocedure. The gNB may use the NSGI in RRC to select an AMF or AMF poolfor the UE. The selected AMF may select the SMFs based on the NSSAI inNAS.

The selected AMF provides the UE with a Temporary ID (Temp ID). The TempID can be used for subsequent Registration requests. The Temp ID canidentify an AMF pool, where any AMF within the AMF pool can be used toserve the UE.

In order to minimize the overall signalling to perform the initialRegistration procedure followed by a Protocol Data Unit (PDU) sessionestablishment, in some embodiments, a combined Registration/PDUEstablishment approach may be adopted where the PDU EstablishmentRequest may be combined with the Registration procedure. For example,these embodiments may be useful for UEs that are set to create a defaultPDU session immediately after the Registration procedure. As anotherexample, combining the PDU Establishment Request with the Registrationprocedure may be a convenient way to provide always-on capability (e.g.eMBB with always-on Internet access). The combined Registration/PDUEstablishment approach reduces the overall time to perform bothRegistration and PDU Session Establishment procedures, and may reducethe necessary signalling over the air and in the core network.

-   Some of the advantages provided by embodiments of this system and    method include:-   the AN (i.e. gNB) does not have to have any awareness of the network    slice configuration deployed.-   The network management for network slicing is simplified since only    the Network Repository Function (NRF) is updated when there are    changes to the network slice configuration.-   The UE can specify one or more PDU sessions to be established during    the initial registration procedure for each service/slice type    requested.

In an implementation, a registration system and method are provided.Although the UE is not aware of the network slice configuration used bythe operator when the UE connects to an Access Node (AN), the UE canindicate the service/slice types (SST) it is capable of and the servicedifferentiator (SD) in the registration request. The AN uses informationprovided by the UE in the RRC message to determine which Access andMobility Function (AMF) to select for the UE.

The UE may not initially require all the supported service types to beconfigured during the initial attach procedure. In this case, the UE canspecify which service types are required initially by indicating therequested SST/SD in the registration request.

The UE may also request that multiple Protocol Data Unit (PDU) sessionsbe established for each SST/SD. The PDU session establishmentinformation is included in the registration request. The PDU sessioninformation includes the Domain Network Name (DNN) for the correspondingSST/SD.

The AMF uses the requested SST/SD to select an appropriate SMF and sendsa PDU session establishment request to the selected SMF to establish aPDU session with the indicated DNN.

The registration procedure is used to attach the UE to the 5G corenetwork, which contains one or more network slices. The UE may obtainservices from multiple network slices simultaneously.

During the registration procedure, the UE sends a registration request,which includes the Network Slice Selection Assistance Information(NSSAI). The NSSAI specifies the slice/service type requested by the UE.The registration request may optionally contain the PDU sessionestablishment request information for each service/slice type requestedby the UE. In some embodiments, the PDU session information may includea parameter to indicate that a default PDU session should be establishedfor the associated slice during the initial Registration procedure.

The NSSAI is sent in the NAS message. The Radio Resource Control (RRC)message includes the Temp ID if it is assigned. Otherwise, for theinitial registration, the RRC message includes the subscriber ID. TheRRC message may also include additional information that may assist theRAN in selecting an AMF for the initial registration. The additionalinformation may include, for example, a pre-configured AMF type or apre-configured Network Slice Group ID (NSGI), which may be astandardized value or a PLMN specific value.

The UE may also be configured by the HPLMN with a Network Slice GroupIndicator (NSGI). This is used by the (R)AN to select an AMF or AMF poolto serve the UE during the initial Registration procedure. Once theserving AMF is selected for the UE, the serving AMF assigns a TemporaryID for the UE. The Temp ID is used by the UE for subsequent Registrationrequests.

The NSSAI included in the NAS message may include:

-   S-NSSAI (multiple S-NSSAI can be included i.e. one for each    slice/service type request)-   Slice/Service type (SST)-   Service Differentiator (SD)

In one embodiment, the S-NSSAI may also include the PDU sessionestablishment parameter, which indicates that a default PDU sessionshould be established for the UE during the initial registrationprocedure. Alternatively, the default PDU session establishmentindicator(s) can be a parameter(s).

In some embodiments, the NSSAI in RRC is a NSGI, and the NSSAI in NASmay be referred to as the Configured or Accepted set of S-NSSAI.

Referring to FIG. 1, an embodiment of a registration procedure isillustrated. In step 100, the UE 10 transmits a registration request tothe serving (R)AN 20. The Registration Request includes the NSSAI in theNAS message, the UE Permanent or Temporary ID (Temp ID), securityparameters. In step 105, the (R)AN 20 selects the AMF based on theinformation in the RRC message, which may include a Temp ID or a NetworkSlice Group ID (NSGI). In step 110, the (R)AN 20 node forwards therequest to the new AMF 30 corresponding to the Temp ID. If there is noTemp ID and no NSGI included in the RRC, or there is no valid Temp ID,then the (R)AN 20 forwards the request to a default AMF.

In optional step 115, the new AMF 30 sends a request to the old AMF 40to obtain the UE's information (UE Permanent ID and MM Context). Inoptional step 120, the new AMF 30 sends an Identity Request to the UE 10if the registration request from step 100 did not include the UEPermanent ID, or if the UE Temporary ID was not provided by the old AMF40 in step 115. In optional step 125, the UE 10 sends an IdentityResponse to the AMF, which includes the UE Permanent ID. In step 130,the new AMF 30 initiates the authentication/security procedure. Inoptional step 135, the new AMF 30 sends an Identity Request to the UE 10if the registration request from step 100 did not include the MEidentity, or if it was not provided by the old AMF 40 in step 115. Instep 140, the new AMF 30 performs the ME identity check with theEquipment Identity Register (EIR) 80. In step 150, the location updateprocedure is performed. In step 155, the new AMF 30 selects SMF(s) 50for the UE 10 based on the S-NSSAI, contained in the NAS message. Instep 160, the new AMF 30 sends a PDU session request to the selectedSMF(s) 50 based on the S-NSSAI. The PDU session establishment requestmay be generated by the UE and included in the NAS request or it may begenerated by the default or serving AMF based on the parameters providedby the UE in the NAS request. Alternatively, the gNB may generate thePDU session establishment request if the UE provides the session relatedparameters in the RRC message. In another embodiment, the UE may providea PDU session establishment indicator for specified S-NSSAI to indicatethat a default PDU session should be established during the initialRegistration procedure. The PDU session parameters may be provided bythe UE or it may be obtained by the subscriber information (i.e. UDM).The PDU session related parameters include the SST/SD or SMF ID and theDNN. In optional step 165, the selected SMF(s) 50 establishes a PDUsession and sends a PDU Session Response to the new AMF 30. In step 170,the new AMF 30 sends a Registration Response to the UE 10. TheRegistration Response includes the RRC Response, which includes the NASResponse. The NAS Response includes the Accepted NSSAI (A-NSSAI),selected SM ID(s) and optionally the PDU Session Response for each PDUsession that was established in step 165. The RRC Response includes theUE Temporary ID corresponding to the selected AMF.

The gNB uses the Temp ID or the NSGI in the RRC message to select anappropriate AMF for the UE on subsequent Registration Requests. If thereis no valid Temp ID or NSGI, the gNB forwards the request to the defaultAMF. There is one default AMF for each gNB.

There are two options for the default AMF:

-   First, the default AMF is only responsible for selecting an    appropriate AMF and forwarding the request to the selected AMF. It    is an isolated function that is not a part of any slice. It has an    interface to other AMFs. In order to ensure the isolation of the    slices, it does not have an interface to the SMFs.-   Second, the default AMF may be a serving AMF that also performs the    AMF selection procedure.

The default AMF selects the serving AMF based on the S-NSSAI included inthe UE's NSSAI. The default AMF queries the Network Repository Function(NRF), which determines an appropriate AMF for the UE based on theprovided S-NSSAI(s) and on the UE's subscription information containedin the Unified Data Management (UDM) function and the network sliceconfiguration information included in the NRF. Once the default AMFselects the appropriate serving AMF, the NAS request message is directlyforwarded to the selected AMF instead of redirecting the message to thegNB.

The selected AMF initiates the authentication/authorization procedureand uses the S-NSSAI to determine which SMFs to select for the UE. TheAMF uses the PDU session information (i.e. PDU session establishmentrequest for the indicated SST/SD and DNN) to determine which PDU sessionestablishment requests to send to the selected SMFs. Alternatively, theAMF forwards the PDU session establishment indicator provided by the UEin the initial Registration procedure to the appropriate SFM(s). TheSMF(s) establish the default PDU session for the UE based on the defaultPDU session information provided by the UE and/or the UDM.

The selected SMFs establish a PDU session and send a PDU sessionresponse to the AMF. The AMF includes the PDU session establishmentresponse in the registration response, which is sent to the UE alongwith the accepted NSSAI (A-NSSAI). The registration response containsthe Temp ID identifying the selected AMF and the A-NSSAI, which includesall of the services that are available for the UE. If the UEde-registers from the network and needs to re-register, the UE sends aregistration request including the Temp ID in RRC and/or the A-NSSAI inNAS.

Referring to FIG. 2, a signalling diagram illustrating an embodiment ofAMF and SMF selection is presented. In step 200 the UE transmits aregistration request (NSSAI) to the gNB. In step 205 the gNB selects theappropriate AMF based on the Temp ID or the NSGI provided by the UE inRRC.

If neither the Temp ID nor the NSGI is available, the gNB may handle theregistration request using default information as illustrated inprocedure 210. In step 212, the gNB transmits the registration requestto a default AMF. In step 214, the default AMF identifies and/or selectsthe appropriate AMF. In step 216, the default AMF transmits theregistration request to the selected AMF. If the Temp ID or NSGI isavailable, the gNB may handle the registration request as illustrated inprocedure 220. In step 222 the gNB transmits the registration requestdirectly to the selected AMF. The transmitted registration request mayinclude the Temp ID or NSGI provided by the UE.

In either case, in step 225 the selected AMF selects the SMF(s). In step230 the selected AMF transmits a registration response to the gNB. Theregistration response may include the Temp ID, and the A-NSSAI. Theregistration response may also include the PDU session response if adefault PDU session is established for the UE. In step 235 theregistration response is forwarded by the gNB to the UE.

The AMF selects the SMFs based on the S-NSSAI included in either theC-NSSAI or the A-NSSAI. The AMF may query the Network RepositoryFunction (NRF) if it is not able to determine the appropriate SMFs.

The NRF includes network function and slice related information requiredto determine the appropriate AMF and SMFs. The NRF is used to determinewhich slices are instantiated and available to the AMF. The NRF isconfigured and updated by the management plane whenever a new networkslice is created or modified. The selected SMFs may also establish a PDUsession if requested in the NAS message. The PDU session request mayinclude the DNN for the corresponding SST/SD and the Session and ServiceContinuity (SSC) mode.

If the UE does not specify PDU session establishment information, thenno PDU session is established during the registration procedure for theindicated service type (e.g. S-NSSAI). The UE may request a PDU sessionafter the registration procedure. Alternatively, a default PDU sessionmay be established for the UE based on the information in the UDM.

If the UE does not specify the S-NSSAI then the UE is assigned thedefault network slice for the UE, which is obtained from thesubscription information. A default PDU session may also be establishedfor the UE.

The NSSAI is sent in both the RRC message and in the NAS message. TheNSSAI in the RRC message is the Temp ID or the NSGI. The NSSAI in theNAS message is a collection of the S-NSSAI. If the NSSAI is the C-NSSAIthen the S-NSSAI is the configured S-NSSAI. Otherwise, if the NSSAI isthe A-NSSAI then the S-NSSAI is the accepted S-NSSAI.

The content of the NSSAI in the RRC and NAS messages is illustrated inFIG. 3. UE sends C-NSSAI in the NAS Request 305 and Temp ID or NSGI inthe RRC Request 310. For the initial attach, the UE does not provide aTemp ID (i.e., the Temp ID is null, it may provide the NSGI or asubscriber ID instead). The NAS information includes a collection ofS-NSSAI, w here each contains the SST/SD. The registration message mayoptionally include multiple PDU Session Requests to a specified DNN foreach S-NSSAI. Alternatively, the message may include parameters forgenerating the PDU session establishment request. In another embodiment,the UE may provide a default PDU session establishment indicator toindicate that a default PDU session should be established for thespecified or associated S-NSSAI.

The gNB selects the AMF based on the Temp ID or NSGI included in the RRCRequest message. If there is no Temp ID and no NSGI or there is no validTemp ID then the gNB sends the N2 request 315 to the default AMF, whichselects a serving AMF. The AMF returns a N2 response 320 to the gNB. TheRRC Response message 325 includes the Temp ID for the selected AMF.

The serving AMF selects the SMFs from the information in the NAS requestmessage 305 containing the S-NSSAI. The serving AMF verifies the UEsubscription information with the UDM. There may be fewer number of SMFsselected than the number of S-NSSAIs, which depends on the network sliceconfiguration.

The AMF sends the PDU Session Request (if included in the NAS Requestmessage or if generated by the AMF based on the PDU session parametersprovided by the UE) to the selected SMFs. Alternatively, the AMF sendsthe default PDU Session Establishment indicator to the selected SMFs toindicate that a default PDU session should be established. The NASresponse 330 from the AMF (containing the A-NSSAI) includes all of theSST/SD available to the UE. The AMF may also send the addresses or IDsof the selected SMFs along with the PDU Session Response. The AMF onlyselects SMFs for the SST/SD the UE requested. The AMF may query the NRFto determine which SMF(s) to select for the UE. The NRF is updated withthe network slice configuration information by the Network Managementsystem whenever the network slice configuration is modified.

In embodiments, the default AMF can be one of the following:

-   A standalone AMF that only performs the AMF selection function. It    is an isolated function that is not a part of any slice. It has an    interface to other AMFs. In order to ensure the isolation of the    slices, it does not have an interface to the SMFs.-   A serving AMF that also performs the AMF selection function.

FIG. 4 illustrates Case 1: Service types A, B and C are on separateslices.

FIG. 5 illustrates Case 2: Service types A and B are on the same slice.Service C is on a separate slice from A and B.

For the above Case 1 and Case 2, the content of the UDM, RRC Request,NAS Request, RRC Response, NAS Response messages is illustrated below:

UDM Information: SST/SD supported = {A,B,C} (RRC Request)    Temp ID =null; // This can be a previously assigned Temp ID    NSGI = AMF group 1(NAS Request)    C-NSSAI = {      S-NSSAI = { SST/SD: A }      S-NSSAI ={ SST/SD: B }    }    PDU_Session_Request(A, DN1)   PDU_Session_Request(A, DN2)    PDU_Session_Request(B, DN3)    Or   C-NSSAI = {      S-NSSAI = { SST/SD: A }      S-NSSAI = { SST/SD: B }   }    Default_PDU_Session_Establishment Indicator (A)   Default_PDU_Session_Establishment Indicator (B) (RRC response)   Temp_ID = xxx; // This is the ID corresponding to the selected AMF(NAS) Response    Accepted NSSAI = {    S-NSSAI = { SST/SD: A }   S-NSSAI = { SST/SD: B }    S-NSSAI = { SST/SD: C }    }    SM-IDs:{SM@A, SM@B}   // Case 1: If services A and B are on separate slices   SM-IDs: {SM@AB, SM@AB} // Case 2: Services A and B have the same SMF   PDU_Session_Response(A, DN1),    PDU_Session_Response(A, DN2)   PDU_Session_Response(B, DN3)    Or    Accepted NSSAI = {      S-NSSAI= { SST/SD: A }      S-NSSAI = { SST/SD: B }    }    SM-IDs: {SM@A,SM@B}    PDU_Session_Response(A, DN-X(default)),   PDU_Session_Response(B, DN-Y(default))

For subsequent requests, the UE includes the assigned Temp ID in RRC.

The gNB forwards the registration message to the default AMF if there isno valid Temp ID and no NSGI. Otherwise, it forwards to the request tothe AMF with the associated Temp ID.

In an alternate embodiment, the default AMF may perform theauthentication/authorization procedure instead of the selected AMF.

In an alternate embodiment, the default AMF may perform theauthentication/authorization procedure in addition to the selected AMF.In some embodiments, the authentication/authorization procedure may besplit between the two AMFs.

In an embodiment, the Radio Access Node ((R)AN) selects the Access andMobility Function (AMF) based only on a Temp ID or NSGI. If there is noTemp ID and no NSGI, or if there is no valid Temp ID, then the (R)ANforwards the Registration request to a default AMF, which performs theAMF selection. The AMF selection procedure uses the Network SliceSelection Assistance Information (NSSAI) and subscription information.

The SMF selection procedure is performed during the Registrationprocedure. The AMF selects the Session Management Function (SMF) basedon the Single-NSSAI (S-NSSAI) and the UE's default configurationinformation included in the subscription information.

PDU Session Establishment requests may be piggybacked onto theRegistration request. The UE may specify multiple PDU sessions to beestablished for each S-NSSAI specified in the NSSAI. In one embodiment,the Registration request may include a default PDU session establishmentindicator for specified S-NSSAI.

A UE needs to register with the network to get authorized to receiveservices, to enable mobility tracking and to enable reachability. TheRegistration procedure is used e.g. when the UE needs to initiallyregister to the 5G system, upon mobility procedure when the UE changesto a new Tracking area (TA) in idle mode and when the UE performs aperiodic update (due to a predefined time period of inactivity), etc.

During the initial registration, the Permanent Equipment Identifier(PEI) is obtained from the UE. The AMF operator may check the PEI withan Equipment Identity Register (EIR). The AMF passes the PEI (e.g. theInternational Mobile station Equipment Identity and SoftwareVersion—IMEISV) to the Unified Data Manager (UDM), to the SMF and thePolicy Control Function (PCF).

Referring to FIG. 6A, an embodiment of a registration procedure ispresented.

In step 600 the UE transmits a registration request to (R)AN: AccessNode (AN) message (AN parameters, Registration Request (Registrationtype, Subscriber Permanent Identifier or Temporary User ID or NSGI,Security parameters, NSSAI, UE 5GCN Capability, PDU session status)).One or more PDU Session Establishment Request messages (S-NS SAT, DomainNetwork Name (DNN), PDU Session ID, Session Management (SM) information)may be piggybacked onto the Registration request or one or more defaultPDU session establishment indicators may be included in the Registrationrequest.

In case of 5G-RAN, the AN parameters include e.g., SUPI or the TemporaryUser ID or NSGI, the Selected Network and NSSAI.

The Registration type indicates if the UE wants to perform an “initialregistration” (i.e. the UE is in non-registered state), a “mobilityregistration” (i.e. the UE is in registered state and initiates aregistration due to mobility) or a “periodic registration” (i.e. the UEis in registered state and initiates a registration due to the periodicupdate timer expired). If included, the Temporary User ID indicates thelast serving AMF. The Security parameters are used for Authenticationand integrity protection. NSSAI indicates the Network Slice SelectionAssistance Information (as defined in clause 5.15 of TS 23.501 [2]. ThePDU session status indicates the available PDU sessions in the UE.

In step 605 AMF selection is performed. If a SUPI is included or theTemporary User ID does not indicate a valid AMF and there is no NSGI,the (R)AN forwards the Registration Request to a default AMF. Thedefault AMF is responsible for selecting an appropriate AMF for the UE.If additional information is provided in the RRC Request, the (R)AN mayselect the AMF.

In step 610 the (R)AN transmits a Registration Request to the selected(“new”) AMF: N2 message (N2 parameters, Registration Request(Registration type, Permanent User ID or Temporary User ID or NSGI,Security parameters, NSSAI)).

When 5G-RAN is used, the N2 parameters include the Location Information,Cell Identity and the RAT type related to the cell in which the UE iscamping.

In step 612 an Information Request may be sent from the new AMF to toold AMF: Information Request to complete the Registration Request.

If the UE's Temporary User ID was included in the Registration Requestand the serving AMF has changed since last registration, the new AMF maysend Information Request to old AMF including the complete RegistrationRequest IE to request the UE's SUPI and MM Context.

In step 614 an Information Response (SUPI, MM Context, SMF information)may be returned by the old AMF to the new AMF in response to theInformation Request 612. The old AMF responds with Information Responseto the new AMF including the UE's SUPI and MM Context. If the old AMFholds information about active PDU Sessions, the old AMF may include SMFinformation including SMF identities and PDU session identities.

In step 616 the AMF may transmit an Identity Request to the UE. If theSUPI is not provided by the UE nor retrieved from the old AMF theIdentity Request procedure is initiated by the AMF sending an IdentityRequest message to the UE. In response to receiving the IdentityRequest, the UE returns an Identity response including the SUPI in step618.

In step 620, the AMF may decide to invoke an AUSF. In that case, the AMFshall, based on the SUPI, select an AUSF.

In step 622, the AUSF shall initiate authentication of the UE and NASsecurity functions. The authentication and security are performed. Theprocedure including AMF relocation, e.g., due to network slicing, mayhappen after step 622.

If the AMF has changed, in step 624 the new AMF transmits to the old AMFan Information Acknowledged message that acknowledges the transfer of UEMM context.

If the authentication/security procedure fails, then the Registrationshall be rejected, and the new AMF sends a reject indication to the oldAMF. The old AMF continues as if the Information Request was neverreceived.

If the PEI was not provided by the UE nor retrieved from the old AMF, instep 626 the Identity Request procedure is initiated by AMF sending anIdentity Request message to the UE to retrieve the PEI.

In optional step 628 the AMF initiates ME identity check with the EIR.

If an update location procedure step 632 is to be performed, in step 630the AMF, based on the SUPI, selects a UDM.

If the AMF has changed since the last registration, or if there is novalid subscription context for the UE in the AMF, or if the UE providesa SUPI which doesn't refer to a valid context in the AMF, in step 632the AMF initiates the Update Location procedure. This will include thatUDM initiates Cancel Location to old AMF, if any. The old AMF removesthe MM context and notifies all possibly associated SMF(s), and the newAMF creates an MM context for the UE after getting the AMF relatedsubscription data from the UDM. In some embodiments, the PEI is providedto the UDM in the Update Location procedure.

In step 634, the AMF, based on the SUPI, may select a PCF.

In step 636 the AMF may transmit a UE Context Establishment Request tothe PCF requesting the PCF to apply operator policies for the UE. Basedon the UE Context Establishment Request, in step 638 the PCF returns tothe new AMF a UE Context Establishment Acknowledged message thatacknowledges the UE Context Establishment Request message.

If the AMF is changed, in step 640 the new AMF notifies each SMF of thenew AMF serving the UE with a N11 Request.

The AMF verifies PDU session status from the UE with the available SMFinformation. In case the AMF has changed the available SMF informationhas been received from the old AMF. The AMF requests the SMF to releaseany network resources related to PDU sessions that are not active in theUE.

Based on the N11 Request, in step 642 the SMFs transmit a N11 Responseto the new AMF. The SMF may decide to trigger e.g. UPF relocation.

If the old AMF previously requested UE context to be established in thePCF, in step 644 the old AMF transmits a UE Context Termination Requestto terminate the UE context in the PCF. The PCF responds by transmittinga UE Context Termination Acknowledged message to the old AMF in step646.

In step 650 the new AMF may select SMF(s) based on the S-NSSAI and UEsubscription information in the UDM.

If PDU Session Establishment Request message(s) (S-NSSAI, DNN, PDUSession ID, SM information) are piggybacked onto the RegistrationRequest, in step 652 the new AMF forwards the PDU Session EstablishmentRequest to the selected SMF(s) using the PDU Session Establishmentprocedure. Alternatively, a default PDU session establishment indicatorfor specified S-NSSAI may be included in the Registration Request. Thenew AMF forwards the default PDU session establishment to the selectedSMF(s).

In step 655 the AMF sends a Registration Accept message (Temporary UserID, Registration area. Mobility restrictions, PDU session status, NSSAI,Periodic registration update timer) to the UE indicating that theregistration has been accepted. Temporary User ID is included if the AMFallocates a new Temporary User ID. Mobility restrictions is included incase mobility restrictions applies for the UE. The AMF indicates the newSMF(s) that were selected for the specified S-NSSAI. The AMF indicatesthe PDU session status to the UE. If PDU Session Establishmentrequest(s) were piggybacked onto the Registration request or if defaultPDU establishment indicators were included in the Registration requestand were sent to the SMF(s) then the PDU Session EstablishmentResponse(s) are included in the response message. The UE removes anyinternal resources related to PDU sessions that are not marked active inthe received PDU session status. If the PDU session status informationwas in the Registration Request, the AMF shall indicate the PDU sessionstatus to the UE. The NSSAI includes the accepted S-NSSAIs. The acceptedS-NSSAIs represent the SST/SD available to the UE for subsequentregistration requests. Alternatively, the AMF may generate the PDUsession response based on the PDU session parameters or the default PDUsession establishment indicator provided by the UE in the RegistrationRequest.

In step 660 the UE sends a Registration Complete message to the AMF toacknowledge if a new Temporary User ID was assigned.

Referring to FIG. 6B, an embodiment of a registration procedure ispresented.

In step 600 the UE transmits a registration request to (R)AN: AccessNode (AN) message (AN parameters, Registration Request (Registrationtype, Subscriber Permanent Identifier or Temporary User ID or NSGI,Security parameters, NSSAI, UE 5GCN Capability, PDU session status)).One or more PDU Session Establishment Request messages (S-NSSAI, DomainNetwork Name (DNN), PDU Session ID, Session Management (SM) information)may be piggybacked onto the Registration request or one or more defaultPDU session establishment indicators may be included in the Registrationrequest.

In case of 5G-RAN, the AN parameters include e.g., SUPI or the TemporaryUser ID or NSGI, the Selected Network and NSSAI.

The Registration type indicates if the UE wants to perform an “initialregistration” (i.e. the UE is in non-registered state), a “mobilityregistration” (i.e. the UE is in registered state and initiates aregistration due to mobility) or a “periodic registration” (i.e. the UEis in registered state and initiates a registration due to the periodicupdate timer expired). If included, the Temporary User ID indicates thelast serving AMF. The Security parameters are used for Authenticationand integrity protection. NSSAI indicates the Network Slice SelectionAssistance Information (as defined in clause 5.15 of TS 23.501 [2]. ThePDU session status indicates the available PDU sessions in the UE.

In step 605 the R(AN) selects an AMF based on the NSGI, if available onthe R(AN). If a SUPI is included or the Temporary User ID does notindicate a valid AMF and there is no NSGI, the (R)AN forwards theRegistration Request to a default AMF. The default AMF is responsiblefor selecting an appropriate AMF for the UE. If additional informationis provided in the RRC Request, the (R)AN may select the AMF.

In step 610 the (R)AN transmits a Registration Request to the selected(“new”) AMF: N2 message (N2 parameters, Registration Request(Registration type, Permanent User ID or Temporary User ID or NSGI,Security parameters, NSSAI)).

When 5G-RAN is used, the N2 parameters include the Location Information,Cell Identity and the RAT type related to the cell in which the UE iscamping.

In step 612 an Information Request may be sent from the new AMF to toold AMF: Information Request to complete the Registration Request.

If the UE's Temporary User ID was included in the Registration Requestand the serving AMF has changed since last registration, the new AMF maysend Information Request to old AMF including the complete RegistrationRequest IE to request the UE's SUPI and MM Context.

In step 614 an Information Response (SUPI, MM Context, SMF information)may be returned by the old AMF to the new AMF in response to theInformation Request 612. The old AMF responds with Information Responseto the new AMF including the UE's SUPI and MM Context. If the old AMFholds information about active PDU Sessions, the old AMF may include SMFinformation including SMF identities and PDU session identities.

In step 616 the AMF may transmit an Identity Request to the UE. If theSUPI is not provided by the UE nor retrieved from the old AMF theIdentity Request procedure is initiated by the AMF sending an IdentityRequest message to the UE. In response to receiving the IdentityRequest, the UE returns an Identity response including the SUPI in step618.

In step 620, the AMF may decide to invoke an AUSF. In that case, the AMFshall, based on the SUPI, select an AUSF.

In step 622, the AUSF or the new AMF shall initiate authentication ofthe UE and NAS security functions. The authentication and security areperformed. The procedure including AMF relocation, e.g., due to networkslicing, may happen after step 622. In some implementations, the AUSFmay initiate authentication. In some implementations, the new AMFinitiates authentication.

If the AMF has changed, in step 624 the new AMF transmits to the old AMFan Information Acknowledged message that acknowledges the transfer of UEMM context.

If the authentication/security procedure fails, then the Registrationshall be rejected, and the new AMF sends a reject indication to the oldAMF. The old AMF continues as if the Information Request was neverreceived.

If the PEI was not provided by the UE nor retrieved from the old AMF, instep 626 the Identity Request procedure is initiated by AMF sending anIdentity Request message to the UE to retrieve the PEI.

In optional step 628 the AMF initiates ME identity check with the EIR.

If an update location procedure step 632 is to be performed, in step 630the AMF, based on the SUPI, selects a UDM.

If the AMF has changed since the last registration, or if there is novalid subscription context for the UE in the AMF, or if the UE providesa SUPI which doesn't refer to a valid context in the AMF, in step 632the AMF initiates the Update Location procedure. This will include thatUDM initiates Cancel Location to old AMF, if any. The old AMF removesthe MM context and notifies all possibly associated SMF(s), and the newAMF creates an MM context for the UE after getting the AMF relatedsubscription data from the UDM. In some embodiments, the PEI is providedto the UDM in the Update Location procedure. In some implementations,interactions between the UDM and the PCF include mobility restrictionrelated information (if any).

In step 634, the AMF, based on the SUPI, may select a PCF. In someimplementations, the Permanent User ID is used for PCF selection.

In step 636 the AMF may transmit a UE Context Establishment Request tothe PCF requesting the PCF to apply operator policies for the UE. Basedon the UE Context Establishment Request, in step 638 the PCF returns tothe new AMF a UE Context Establishment Acknowledged message thatacknowledges the UE Context Establishment Request message.

If the AMF is changed, in step 640 the new AMF notifies each SMF of thenew AMF serving the UE with a N11 Request.

The AMF verifies PDU session status from the UE with the available SMFinformation. In case the AMF has changed the available SMF informationhas been received from the old AMF. The AMF requests the SMF to releaseany network resources related to PDU sessions that are not active in theUE. In some implementations, the AMF performs the PDU session statuslogic. In some implementations, each SMF performs the PDU session statuslogic.

The UE may include PDU session information in the Registration Requestfor the initial Registration procedure to indicate that a default PDUsession should be established for the specified S-NSSAI(s). The PDUsession information should identify the network slice (e.g. S-NSSAI) forthe default PDU session. The AMF forwards the request to the selectedSMF(s). The SMF(s) may obtain additional PDU session information fromthe UDM (e.g. DNN, Session and Service Continuity (SSC) mode) to triggera PDU Session Establishment procedure. In some implementations, the PDUSession Establishment procedure is performed as defined in clause4.3.2.2.1 (steps 4-8) of TS 23.501 (incorporated herein by reference).

Based on the N11 Request, in step 642 the SMFs transmit a N11 Responseto the new AMF. The SMF may decide to trigger e.g. UPF relocation.

If the old AMF previously requested UE context to be established in thePCF, in step 644 the old AMF transmits a UE Context Termination Requestto terminate the UE context in the PCF. The PCF responds by transmittinga UE Context Termination Acknowledged message to the old AMF in step646. If the Registration type indicated by the UE is a periodicregistration update, then steps 644 and 646 may be omitted.

In step 655 the AMF sends a Registration Accept message (Temporary UserID, Registration area. Mobility restrictions, PDU session status, NSSAI,Periodic registration update timer) to the UE indicating that theregistration has been accepted. Temporary User ID is included if the AMFallocates a new Temporary User ID. Mobility restrictions is included incase mobility restrictions applies for the UE. The AMF indicates the newSMF(s) that were selected for the specified S-NSSAI. The AMF indicatesthe PDU session status to the UE. In implementations where the PDUSession Establishment request(s) were piggybacked onto the Registrationrequest or if default PDU establishment indicators were included in theRegistration request and were sent to the SMF(s) then the PDU SessionEstablishment Response(s) are included in the response message.

The UE removes any internal resources related to PDU sessions that arenot marked active in the received PDU session status. If the PDU sessionstatus information was in the Registration Request, the AMF shallindicate the PDU session status to the UE. The NSSAI includes theaccepted S-NSSAIs. The accepted S-NSSAIs represent the SST/SD availableto the UE for subsequent registration requests. Alternatively, the AMFmay generate the PDU session response based on the PDU sessionparameters or the default PDU session establishment indicator providedby the UE in the Registration Request.

In implementations where PDU session establishment is performed in step640, the New AMF may include an N2 PDU session request message with theRegistration Accept message sent in step 655. In the implementations,receipt of the Registration Accept may trigger, in step 656, AN-specificsignalling exchange (RRC Connection Reconfiguration for 3GPP RAN case)between the UE and the R(AN) to establish necessary AN resources for theUE. In some implementations, the NSSAI may be provided to the (R)AN bythe new AMF.

If PDU Session Establishment Request message(s) (S-NSSAI, DNN, PDUSession ID, SM information) are piggybacked onto the RegistrationRequest, in step 658 the new AMF forwards the PDU Session EstablishmentRequest to the selected SMF(s) using the PDU Session Establishmentprocedure. Alternatively, a default PDU session establishment indicatorfor specified S-NSSAI may be included in the Registration Request. Thenew AMF forwards the default PDU session establishment to the selectedSMF(s).

In step 660 the UE sends a Registration Complete message to the AMF toacknowledge if a new Temporary User ID was assigned.

Referring to FIG. 7, an embodiment of a registration procedure with AMFrelocation is presented. When an AMF receives a Registration request,the AMF may need to reroute the Registration request to another AMF,e.g. due to network slicing is used and the initial AMF is not theappropriate AMF to serve the UE. The Registration with AMF relocationprocedure, is used to reroute the NAS message of the UE to the targetAMF during a registration procedure.

The initial (first) AMF and the target (second) AMF register theircapabilities at the NRF.

In step 705, the (R)AN sends the Initial UE message to the first AMF.The Initial UE message carries a Non-Access Stratum (NAS) Registrationmessage (FIG. 6). The first AMF is the default AMF if there is no validTemporary ID and there is no NSGI. Otherwise, the first AMF is theappropriate serving target AMF.

In step 710, if the default AMF is not the appropriate target AMF thenthe default AMF decides to reroute the NAS message to another AMF. Thedefault AMF sends an NF discovery request, which includes the NSSAI, tothe NRF to find a proper target AMF that has required capabilities toserve the UE.

In step 715, based on the information about registered NFs and requiredcapabilities, a target AMF is selected and the NRF transmits a NFdiscovery response identifying the target AMF.

If the initial AMF, based on NSSAI, local policy and subscriptioninformation, determines to forward the NAS message to the target AMFdirectly, in procedure 720 the initial AMF sends Reroute NAS message tothe target AMF in step 722. The Reroute NAS message includes theinformation about N2 terminating point for (R)AN and the NAS messagecarried at step 705. If network slicing is used and the initial AMFupdates the NSSAI at step 705, the updated NSSAI is included in theredirection NAS message and procedure 725 is skipped.

If the initial AMF, based on local policy and subscription information,determines to forward the NAS message to the target AMF via (R)AN, inprocedure 725 the initial AMF sends Reroute NAS message to the (R)AN instep 727. The Reroute NAS message includes the information about thetarget AMF and the NAS message carried at step 705. If network slicingis used and the initial AMF updates the NSSAI at step 705, the updatedNSSAI is included in the redirection NAS message. In step 729, based onthe Reroute NAS message the (R)AN sends the Initial UE message to thetarget AMF.

After receiving the first NAS message transmitted at procedure 720 or725, in step 735 the target AMF sends to the (R)AN the Initial UEcontext setup request which includes information about the N2terminating point for target AMF and a new Temp ID assigned by thetarget AMF is also included.

In step 740 (R)AN sends the Initial UE context response to the targetAMF.

FIG. 8 is a block diagram of an embodiment of a computing system 800that may be used for implementing the devices and methods disclosedherein. In particular, the network nodes may each include one or morecomputing systems 800. The network functions described above may beinstantiated by execution on one or more computing systems 800. In someembodiments, a network function may be instantiated across a pluralityof computing systems 800 across a plurality of geographic locations. TheUE described above may comprise a computing system 800 adapted toperform the methods described herein.

Specific devices may utilize all of the components shown or only asubset of the components, and levels of integration may vary from deviceto device. Furthermore, a device may contain multiple instances of acomponent, such as multiple processing units, processors, memories,transmitters, receivers, etc. The computing system 800 includes aprocessing unit 802. The processing unit 802 typically includes acentral processing unit (CPU) 814, a bus 820 and a memory 808, and mayoptionally also include a mass storage device 804, a video adapter 810,and an I/O interface 812 (shown in dashed lines). The computing system800 may further include one or more network interface(s) 806 forconnecting the computing system 800 to communication networks 822.

The CPU 814 may comprise any type of electronic data processor, and mayinclude one or more cores or processing elements. The memory 808 maycomprise any type of non-transitory system memory such as static randomaccess memory (SRAM), dynamic random access memory (DRAM), synchronousDRAM (SDRAM), read-only memory (ROM), or a combination thereof. In anembodiment, the memory 808 may include ROM for use at boot-up, and DRAMfor program and data storage for use while executing programs. The bus820 may be one or more of any type of several bus architecturesincluding a memory bus or memory controller, a peripheral bus, or avideo bus.

The mass storage 804 may comprise any type of non-transitory storagedevice configured to store data, programs, and other information and tomake the data, programs, and other information accessible via the bus820. The mass storage 804 may comprise, for example, one or more of asolid state drive, hard disk drive, a magnetic disk drive, or an opticaldisk drive.

The video adapter 810 and the I/O interface 812 provide optionalinterfaces to couple external input and output devices to the processingunit 802. Examples of input and output devices include a display 818coupled to the video adapter 610 and an I/O device 816 such as atouch-screen coupled to the I/O interface 812. Other devices may becoupled to the processing unit 802, and additional or fewer interfacesmay be utilized. For example, a serial interface such as UniversalSerial Bus (USB) (not shown) may be used to provide an interface for anexternal device. Alternatively, the computing system 800 may rely uponthe network interface(s) 806 for connection to available massstorage(s), video adapter(s) 610, and I/O interface(s) 812 available onthe networks 822.

Based on the foregoing description, embodiments of the present inventionmay provide any one or more of:

-   A method for registering a User Equipment (UE) for connection to a    service available on a network, the method comprising:    -   receiving a registration request from the UE;    -   selecting an access and mobility function (AMF) of the network        based on the registration request;    -   transmitting the registration request to the selected AMF;    -   receiving a registration response from the selected AMF; and,    -   transmitting the received registration response to the UE.-   In some embodiments, the AMF is selected based on a temporary    identifier assigned to the UE or a Network Slice Group Indicator.-   In some embodiments, the AMF is selected by transmitting the    registration request to a default AMF for selection of the selected    AMF.-   In some embodiments, the network comprises an access node.-   In some embodiments, the access node transmits the registration    request directly to the selected AMF.-   In some embodiments, the access node includes the temporary    identifier or the Network Slice Group Indicator with the    registration request.-   A method in an access and mobility function (AMF) of a network, the    method comprising:    -   receiving, by the AMF, a registration request pertaining a User        Equipment (UE) connected to an access node of the network;    -   at least partially in response to the registration request:        -   interacting with a Network Repository Function (NRF), using            information in the received registration request to obtain            network slice configuration information pertaining to the            UE;        -   identifying a second AMF based at least in part on the            obtained network slice configuration information; and        -   forwarding the registration request to the second AMF.

Although the present application describes specific features andembodiments, it is evident that various modifications and combinationscan be made thereto without departing from the invention. Thespecification and drawings are, accordingly, to be regarded simply as anillustration as defined by the appended claims, and are contemplated tocover any and all modifications, variations, combinations or equivalentsthat fall within the scope of those claims.

We claim:
 1. A method in an access and mobility function (AMF) of anetwork, the method comprising: receiving, by the AMF, a Non-AccessStratum (NAS) registration request pertaining a User Equipment (UE)connected to the access node; at least partially in response to theregistration request: registering the UE on the network; andestablishing a Protocol Data Unit (PDU) session for the UE, based oninformation contained in the registration request; and transmitting, bythe AMF, a registration response to the UE.
 2. The method of claim 1,wherein the NAS registration request is received from either one of: anaccess point of the network associated with the UE; and a second AMF ofthe network.
 3. The method of claim 1, wherein the NAS registrationrequest comprises a PDU session request, and the step of establishingthe PDU session for the UE comprises establishing the PDU session inaccordance with the PDU session request.
 4. The method of claim 3,wherein the PDU session request comprises any one or more of: a SliceService Type (SST); a Service Differentiator (SD); a Network SliceSelection Assistance Information (NSSAI) indication; and a DomainNetwork Name (DNN).
 5. The method of claim 3, wherein establishing thePDU session in accordance with the PDU session request comprises:transmitting the PDU session request to a selected Session ManagementFunction (SMF) of the network; and subsequently receiving a PDU sessionacknowledgment message from the selected SMF.
 6. The method of claim 1,wherein the step of establishing the PDU session for the UE comprisesestablishing a default PDU session.
 7. The method of claim 6, whereinestablishing the default PDU session comprises: obtaining subscriptioninformation associated with the UE from a Unified Data Management (UDM)function of the network; and establishing the default PDU session inaccordance with the obtained subscription information.
 8. The method ofclaim 7, wherein the obtained subscription information comprises any oneor more of: a Network Slice Selection Assistance Information (NSSAI)indication associated with the UE; a Domain Network Name (DNN); and aSession and Service Continuity (SSC) mode associated with the UE.
 9. Themethod of claim 7, wherein establishing the default PDU session inaccordance with the obtained subscription information comprises:transmitting a PDU session request message to a selected SessionManagement Function (SMF) of the network, using the obtainedsubscription information; and subsequently receiving a PDU sessionacknowledgment message from the selected SMF.
 10. A method in an accessnode of a network, the method comprising: receiving, by the access node,a Radio Resource Control (RRC) message containing a registration requestfrom a User Equipment (UE) connected to the access node; at leastpartially in response to the registration request: selecting an accessand mobility function (AMF) based on information in the receivedregistration request; and subsequently forwarding a corresponding NonAccess Stratum (NAS) registration request to the selected AMF, the NASregistration request including PDU session request informationpertaining to the UE.
 11. The method of claim 10, wherein the PDUsession request information comprises any one or more of: a temporaryidentifier associated with the UE; a Slice Service Type (SST); a ServiceDifferentiator (SD); a Network Slice Selection Assistance Information(NSSAI) indication; and a Domain Network Name (DNN).
 12. The method ofclaim 10, wherein the selected AMF is selected based on either one of atemporary identifier associated with the UE and a Network Slice GroupIndicator.
 13. The method of claim 10, wherein the selected AMF is apredetermined default AMF.
 14. A User Equipment (UE) comprising: atleast one processor; and a non-transitory computer readable storagemedium storing software instructions configured to control the at leaston processor to: generate a Radio Resource Control (RRC) messagecontaining a registration request for registering the UE for connectionto a service available on a network, the registration request furtherincluding PDU session request information; transmit the RRC message toan access point of the network; and subsequently receive a registrationacknowledgment from an access and mobility function (AMF) of thenetwork.
 15. The UE of claim 14, wherein the PDU session requestinformation comprises any one or more of: a temporary identifierassociated with the UE; a Slice Service Type (SST); a ServiceDifferentiator (SD); a Network Slice Selection Assistance Information(NSSAI) indication; and a Domain Network Name (DNN).